The transformation comes after he lost 30lbs last year to play sociopath Lou Bloom in Nightcrawler for which he has just a won a Spirit Award nomination.

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Unrecognizable: Jake Gyllenhaal has piled on the muscle for his role as a boxer in upcoming movie Southpaw

Half the man: Jake as Lou Bloom in Nightcrawler for which he lost 30lbs but won a Spirit Award nomination

The actor dropped the pounds with a strict calorie counting diet, he told Variety at the time.

'I would try to eat as few calories as possible. I knew if I was hungry that I was in the right spot.'

But now he's gone from one extreme to the other adding 15lb of muscle to his usual weight to play Billy 'The Great Hope' - a left handed boxer who stages a comeback from personal tragedy.

The single still from Southpaw obtained by Deadline shows the Oscar nominated actor shirtless and fighting in the ring.

His tattooed torso is ripped and his arms are pumped with muscle.

'Jake is going to change how people see him,' director Antoine Fuqua told Deadline.

'I had him training twice a day in the boxing ring, he did two-a-days seven days a week. I pretty much had him with me and my trainer every day.

'I took him to almost every fight. I had him train at Floyd Mayweather’s gym in Vegas and we watched Floyd’s fights, and the Manny Pacquiao fight.'

He added: 'He trained in New York at Church Gym with real fighters. We literally turned him into a beast.

'Jake, my God, he’s a very electric, powerful fighter in this movie, and a guy who fights for his daughter.

'I’m confident that this will change how people see Jake, as a leading man.

'He was training like a fighter. I had him sparring, really getting hit. I put him in situations where I wanted to see what he was made of. No one but fighters understand the sacrifice it takes to be a fighter.'

Southpaw is set for release next year.

Spot the difference: Jake pictured shirtless on the beach in Hawaii in 2011 looking a lot less muscley